The regulation of the family of UDP glucuronosyltransferase enzymes is being studied at the level of RNA, DNA and protein chemistry. Transferase activities toward certain substrates are known to be induced by different types of effector compounds: such compounds used in these studies include phenobarbital (PB), 3-methylcholanthrene (MC) and clofibrate (CF). We have purifed 10-15 different mouse and 6-8 different human transferase cDNA clones by specific antibody reactivity with fushion proteins produced by the appropriate cDNA library constructed in the lambda gt11 vector. One of the mouse clones, pUDPGTm-5, contains a 2.4 Kb insert and encodes an MC-regulated mRNA. The cDNA has been nearly completely sequenced and has been used as a probe to isolate the corresponding genomic clones from a mouse genomic library in Charon-4A phage. The genomic clones are being restricted in preparation for sequencing the 5' upstream region and the exon-intron junctions. The mouse cDNA, UDPGTm-1, (previously charaterized with respect to nucleotide sequence, deduced amino acid sequence, signal peptide, transmembrane spanning region and mRNA regulation) was inserted into two different yeast vectors, transfected into two different host cells, and is shown by Western blot analysis to express a transferase protein (Mr = 68,856). Studies are in progress to determie the substrate specificity of the transferase. The expression in yeast should make it possible for us to determine the substrate specificity for each transferase cDNA clone. One human cDNA UDPGTh-1 (2.5 Kb) encoding a 2500-nt mRNA (shown to have a high degree of similarity to UDPGTm-1) is about 75% sequenced and is being prepared for transfection into yeast for expression studies. The orphan drug (in USA) Zixoryn (flumecinol) administered to newborns in certain countries to prevent neonatal jaundice is shown in our laboratory (in mice and rats) for the first time to induce specifically bilirubin transferase activity.